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Routing question

Discussion in 'Networks' started by Eatskittens, Feb 17, 2010.

  1. Eatskittens

    Eatskittens New Member

    I have a question. If there are 2 networks connected by router. And on one network a host is configured with an incorrect GW can hosts from the other network communicate with it? If not could you tell me why?
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  2. soundian

    soundian Gigabyte Poster

    That's got me thinking.
    If the host (Host A) with the incorrectly configured GW is on the same subnet as the GW, then the other host (host B) should be able to send it packets. Host A should then return them to the actual GW, because as far as it knows, that's where they originated.
    However, if host A tries to initiate contact with host B, the router will ignore the packets because they aren't addressed to it.
    So, if I'm right, they can communicate only if host B intitiates the connection.

    Now I'm gonna run for cover as the experienced guys tear holes in my logic.
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  3. BosonMichael
    Highly Decorated Member Award

    BosonMichael Yottabyte Poster

    If there's no route, there's no way to get to the destination.
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  4. SimonD
    Honorary Member

    SimonD Terabyte Poster

    As Michael said, with no route out from the host it won't go outside of it's own network segment.
    That's the idea of the 'GATEWAY', it's a gateway to other places.

    What will happen is that if the machine with the correct gw address pings, it won't actually receive any replies back so will get a non reply (rather than host unreachable, it will be like ICMP packets have been dropped at a firewall.

    If the host that has the incorrect gw configured tries to ping he should get a destination host unreachable message because all it knows about is it's local subnet and it has no way to go beyond it's own boundaries.

    That's the logic behind tracert or pathping, it can tell you to a certain degree where packets are being dropped.
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  5. Sparky
    Highly Decorated Member Award

    Sparky Zettabyte Poster Moderator

    No, because the traffic will not be able to route back the way to the original host that made the request.
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  6. beaumontdvd

    beaumontdvd Kilobyte Poster

    That has helped me understand about gateways I didn't know any of that. thanks mate, worded it perfect.

    Reppped :biggrin

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  7. danielno8

    danielno8 Gigabyte Poster


    just to clarify, the packet host A recieved will be addressed with a source IP of host B (which is on a different subnet). As it is on a different subnet, it will send to the incorrect GW and fail to reach host B.
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